1. Field of the Invention
The present invention refers to apparatuses for detecting and measuring the level of a fluid stored inside a container or a tank. More specifically, the present invention refers to an apparatus for measuring the level of a liquid fuel in a tank in an automobile vehicle. In addition to measuring and indicating the volume of fuel, the apparatus according to the present invention may also provide an indication of the quality if the fuel in the tank and/or the ratio between the two different types of fuels, in the case of bi-fuel engines.
2. Description of the Prior Art
Typically, an internal combustion engine uses a liquid fuel such as diesel, kerosene, gasoline, alcohol and others, or even more than one type of these mentioned fuels, such as it is the case of bi-fuel engines, which fuels are stored in a tank that is separate from the engine.
These tanks are designed to store a volume of fuel sufficient to ensure a sustained operation of the engine. That is, automobiles are traditionally manufactured with fuel tanks having a storage capacity sufficient to ensure a continuous operation to allow it to run for at least a few hundreds kilometers.
In order to provide the driver a safe information regarding the autonomy of the vehicle or, in another words, what distance can still be covered with the volume of fuel in the tank, vehicles are usually provided with monitoring devices that continuously measure and indicate the amount of fuel left in the tank to inform driver about the need to refuel before exhausting all the fuel in the tank.
Generally speaking, a typical monitoring system comprises a measuring unit positioned within the fuel tank and an indicating gauge in a location remote from the tank, usually on the dashboard of the vehicle. The measuring unit determines the level of the fuel in the tank and sends a signal representative of this level and/or volume of fuel to the gauge in the dashboard, typically a dial that provides a visual indication of the amount of fuel left in the tank.
An automobile vehicle typically includes in its dashboard a fuel gauge having a pointer which gradually oscillates between the positions “full” and “empty” on the dial itself, as the vehicle moves from A to B thus indicating the volume of fuel left in the tank.
Traditional measuring units comprises a floating element such as a buoy, usually made of foam, coupled through a metallic rod to a variable resistance which acts as a potentiometer. As the buoy floats in the fuel, as the level of the fuel inside the tank varies, the position of the buoy and, consequently, the position of the metallic rod over the variable resistance also vary, therefore generating a variable voltage signal depending on the position of the buoy and on the angular inclination of the metallic rod which indicates the relative level of fuel in the tank.
The variable resistance is typically manufactured with a technology of conductive and resistive tracks deposition of a thick film over a ceramic substrate. Depending on the constructive form, this variable resistor operates immersed in the fuel itself or dry protected in a sealed off quenched chamber. This resistive component is commonly known simply as a “thick film”.
As each vehicle has a geometric peculiar and particular tank design, the resistance is designed to compensate the non linearity of the relation between the level of the liquid and the volume of liquid effectively left in the tank, to allow the resulting signal to be effectively proportional to the volume of the fuel.
This linearity function of the relation between the liquid level and the liquid volume existing in the tank, duly represented by the variations in the resistive elements of the “thick film”, makes each and every measuring unit something unique for each and every determined model of a vehicle thus stopping its usage in another vehicle which presents any difference in the geometry in relation to the very one for which it was designed.
A first and serious inconvenience of this measuring system comprising a buoy, a metallic rod and a variable resistance is exactly the very inadaptability of the measuring unit to other tanks designs.
Another serious inconvenience of this measuring system which comprises a buoy, a metallic rod and a variable resistance is the fact that it is easily influenced by any dislocation of the vehicle from a position of being totally plan.
Every time the vehicle changes from a substantially horizontal position, such as when the vehicle is going up or down a hill, the fuel level inside the tank varies and this variation truly affects the measuring being effected by the buoy's system, the metallic rod and the variable resistance.
While in normal traffic conditions this distortion is at least partially compensated by the frequent variations in the horizontal positioning of the vehicle, when it is in a relatively long uphill or downhill stretch this distortion may even cause a dry spell.
Another rather serious inconvenience of this measuring system is the fact that, in a general manner, the liquid fuels utilized are highly aggressive, something which could result in a mal functioning of the buoy, metallic rod and variable resistance system that generates non-correct measured levels of fuel.
Additionally, the mechanical nature of this very buoy, metallic rod and variable resistance system could also result in non-correct indications of the fuel level in the fuel tank. For example, the connection between the rod and the variable resistance and/or the very geometry of the tank could impose limitations to the rod's movement and thus the buoy could be partially submersed inside the fuel thus providing an inaccurate measurement.
Similarly, inaccuracy could take place when the amount of fuel present in the tank is very small, because of the fact that frequently the buoy's course does not extend down to the most inferior parts of the tank and thus the measuring unit sends an information to the exhibition panel which does not correspond to the reality because it indicates an empty tank whilst there could be a few liters left in its interior.
And as if the above-mentioned problems were not enough, the last few years have witnessed an increasing rise in the complexity of automobile vehicles projects and designs.
For example, with a view to increase the internal space of the cabin compartment, the designers are placing the different components of the vehicle in places where beforehand the utilization was simply unimaginable.
For the specific case of fuel tanks, the possibility of the utilization of materials of an easier moulding and resistance to the corrosive attack of fuels has opened the doors for an unnumbered amount of projects and designs of tanks, with the most different formats which permits to the designers a maximum utilization of the available space whilst maximizing the size of the tank and all that means we are frequently facing fuel tanks of the least conventional formats and shapes.
Therefore, due to the considerations of space and aerodynamics the tanks can be conformed in order to fit around the parts of the body or the chassis of the automobile, something that practically makes it unfeasible the utilization of the traditional buoy, metallic rod and variable resistance system in these tanks.
Evidently some safety regulations must be observed but in practical terms apart from the means to measure the level of fuel the only effective demand with regards to the project of a fuel tank for an automobile vehicle is that the feeding aperture be placed in such a manner as to permit an easy access and an easy insertion of the fuel pump pipe mouthpiece.
U.S. Pat. No. 6,880,398, of Apr. 19, 2005, discloses a fuel level inside a tank detection system coupled or integrated to a fuel pump that can be utilized in a variety of formats and sizes of tanks.
According to this patent the device comprises a body and a level of fuel detection unit, which body is configured being positioned inside the tank and it defines a plurality of coupling stages. The fuel level detection unit comprises a base, a buoy and an articulated element joining the buoy to the base in a similar form to the normal measuring unit and it is capable of being selectively coupled to each one of the coupling stations.
Still with regards to fuel level measuring systems inside a tank with mobile parts, other solutions can be the use of angle sensors substituting the “thick film” potentiometer and/or the techniques of inductive bridge with captive fluctuation (sliding in cavities). These two solutions are advantageous due to the fact of the sealing off and quenching between the captive fluctuation gadget itself (and its mechanism) and the sensor circuit.
However, due to the increasing difficulty of utilizing a buoy, rod and variable resistance measuring system, other solutions have been developed for the monitoring and for the measuring of the fuel level inside a fuel tank in an automobile vehicle.
U.S. Pat. No. 6,907,780, of Jun. 21, 2005 describes a method and an apparatus to determine the amount of fuel inside a tank by monitoring the pressure conditions and the temperature of the tank. An independent and separated air space is created and by monitoring the pressure conditions and the isolated space temperature and the pressure conditions and the temperature in the rest of the tank, the amount of fuel in it can be determined.
U.S. Pat. No. 6,871,540, of Mar. 29, 2005 describes a method and an apparatus to determine the amount of unloaded fuel from a tank through a system line, the difference between the amount of fuel originally stored inside the tank before unloading being calculated in order to indicate the amount of fuel inside the tank.
The forms of transducer which can promise the best solution for this problem are: optic, ultra sound and capacitive.
The use of any form of light in order to determine the level is confronted by the utilization of elements which transparency must be kept within the set, a difficult task indeed considering the accumulation of impurities that can occur within the tank.
Even though optical techniques such as photometry, colorimetry, nephelometry and refractometry can be considered in the future in order to determine the physical characteristics of the fuel, as long as they are duly coupled to a mechanism of automatic cleansing of the optical element in contact with the fluid.
The most easily viewed form in industry for the cleansing of these elements is the ultra sound, but a fuel level indicator with an accessible cost probably could not support its additional cost by the automobile industry, for the ultra sound and capacitance seems to be the two left ways.
The capacitive level sensors are widely known in the industrial instrumentation in general and it has already found a greater utilization in the past but it significantly lost ground to more modern versions based on ultra sonic transducers.
In order to understand this very substitution it is necessary to remember and to consider that in industry the level measured are much greater than the ones found in automotive fuel tanks. Storage tanks for liquids, solids and pastes in an industrial environment normally present great dimensions, frequently measuring many meters in height and contain between hundreds and thousands of kilos of material. As the capacitive transducers must be immersed in the product to be measured so that it may work, it ends up facing serious cost problems, corrosion protection, mechanical strength, geometry and others.
These very restrictions disappear when the volume to be measured is small—as it is the case of fuel tanks of automobile vehicles—thus making the utilization of capacitive level sensors competitive in relation to ultra sound.